Everyone as well as women desire to have a beautiful skin. Therefore, under present circumstances, most women try to keep the skin in preferable conditions, using cosmetics and the like. The skin conditions vary largely depending upon the individuals. The skin aging is roughly classified into physiological aging (original physiological aging) that occur in every human being along with aging, and pathological aging caused by UV light (damage caused by UV light, or photoaging) (for example, see Non-patent Document 1).
Due to the skin aging, changes with time, such as the loss of elasticity and the increase in wrinkles occur, which have a great influence on the appearance and impression. Such changes with time reflect the physiological changes among the skin, in particular, in the epidermis and dermis constituting the skin, and for example, shallow wrinkles are greatly influenced by the epidermis and papillary layer, whereas deep wrinkles and sagging are greatly influenced by the dermis (for example, see Non-patent Document 2). Thus, in order to keep the skin beautifully, it is very important to judge the conditions such as each thickness of the epidermis and dermis objectively and quantitatively, which makes it possible to select and use appropriate cosmetics and medicine suitable for the skin conditions, or conduct doctor's treatment and the like.
As such a method of measuring physiological or aging changes of a skin, a method of estimating an actual age by measuring an external appearance of wrinkles or sagging (for example, see Patent Documents 1 and 2), a method of estimating a skin age based on the measurement results of a skin surface form (for example, see Patent Document 3), a method of calculating a skin age based on changes in vibration obtained when a skin is brought into contact with a vibrator (for example, see Patent Document 4), a method of estimating an age based on the dermal brightness from an ultrasonic skin image (for example, see Patent Document 5), a method of evaluating the stiffening effect of a skin based on the thickness of the skin from an ultrasonic image (for example, see Patent Document 6), and the like are disclosed. Further, a method of estimating an age using an average area of a horny layer cell of a epidermis as an index (for example, see Patent Document 7), a method of evaluating the degree of skin aging by measuring changes in a force generated by a fibroblast (for example, see Patent Document 8), a method of evaluating the degree of skin aging using a DNA (for example, see Patent Document 9), and the like are disclosed. However, none of the above discloses a method of determining damage caused by UV light and physiological aging, and a method of estimating each thickness of an epidermis and a dermis objectively and quantitatively.
In recent years, a procedure of measuring a near infrared absorption spectrum of a tissue, a skin, and a hair of a human being, performing a statistical treatment (multivariate analysis) such as multiple regression analysis and principal component analysis with respect to spectrometry and specific values such as moisture and a tissue state, and based on a correlation thereof, clarifying a skin moisture, mammitis, hair conditions, and the like noninvasively has been known (for example, see Patent Documents 10-13). Further, quantification of the existing amount of dermal collagen of a skin (for example, see Patent Document 14). However, none of those discloses a method of determining skin damage caused by UV light and physiological aging, and a method of estimating each thickness of an epidermis and a dermis objectively and quantitatively.
Under such circumstances, the inventors of the present invention have found, in judging the skin conditions such as a skin thickness, a skin surface form, a skin viscoelasticity, or skin internal tissue structure, that the thickness of a skin can be judged noninvasively by using multivariate analysis of a near infrared absorption spectrum, and filed a patent application (Patent Document 15). In order to select and use appropriate cosmetics and medicine suitable for skin conditions, there is a demand for developing means for further advancing this technology, and measuring each thickness of an epidermis and a dermis constituting a skin noninvasively and objectively.
Patent Document 1: JP 2002-330943 A
Patent Document 2: JP 2002-360544 A
Patent Document 3: JP 2005-095326 A
Patent Document 4: JP 2001-212087 A
Patent Document 5: JP 2000-083954 A
Patent Document 6: JP 11-290315 A
Patent Document 7: JP 11-299792 A
Patent Document 8: JP 2004-354159 A
Patent Document 9: JP 2001-161364 A
Patent Document 10: JP 2002-090298 A
Patent Document 11: JP 2003-344279 A
Patent Document 12: WO 01-075421 A
Patent Document 13: JP 2003-270138 A
Patent Document 14: JP 2005-083901 A
Patent Document 15: JP 2005-034350 A
Non-patent Document 1: “Utility of Cosmetics” edited by THE SOCIETY OF COSMETIC CHEMISTS OF JAPAN, Yakuji Nippo Ltd., 51-52, 2001
Non-patent Document 2: “Utility of Cosmetics” edited by THE SOCIETY OF COSMETIC CHEMISTS OF JAPAN, Yakuji Nippo Ltd., 163, 178, 2001